1. Field of the Invention
This invention relates to electromechanical relays for switching high-frequency signals with high reliability, long service life, stable insertion loss, stable return loss and high isolation.
2. Description of the Prior Art
Many different types of switches are known for the switching of radio frequency signals. Two main varieties of radio frequency switches are known as reflective switches and absorptive switches, wherein a reflective switch provides an open circuit termination at the output “off” port or terminal and an absorptive switch provides a 50-ohm termination at the output port or terminal. The ideal choice of switch type depends on the application. Radio frequency switches, as with other types of electrical switches, are made in configurations including but not limited to single pole double throw, single pole triple throw, single pole sextuple throw and matrix or transfer type switches. An example of a matrix or transfer type switch is shown in U.S. Pat. No. 4,908,588.
For actual switching function, the switch mechanisms include spring actuated contacts, electromagnetic actuators, plungers with permanent magnets, articulated joints and other movable elements. Examples of these types of switches and switching mechanisms are shown in U.S. Pat. Nos. 6,414,577, 6,340,923, 6,337,612, 6,211,756, 6,204,740, 6,124,771, 5,894,255, 5,815,049, 5,724,014, 5,699,030, 5,652,558, 5,499,006 and 5,272,458. Unfortunately, these switches suffer from poor reliability and low switch lifetime.
Other examples of radio frequency (RF) switches are shown in U.S. Pat. Nos. 6,133,812, 6,037,849, 4,908,588, 4,697,056 and 4,298,847. The RF switches shown in these patents use multiple cylindrical guide pins to guide the reed conductors in an up and down motion while preventing contact between the reed conductors and the walls of the surrounding RF channel.
Guide pin wear, resulting in debris generation and undesirable reed movement, is known to be a major source of performance degradation and operational failure in RF switches and limits the working cycle life of the switch. One method to reduce wear of the guide pins is to increase the contact area between the guide pins and the conductor reeds. This method is illustrated in U.S. Pat. Nos. 5,815,057 and 5,642,086. Another RF switch with increased guide pin contact area is shown in U.S. Pat. No. 6,650,210. The guide element taught therein is generally U-shaped and made from a low-friction polymer material to increase the contact area without increasing sliding friction. However, in the construction of this switch the location of the conductor reeds is controlled by features formed in a case portion of the switch body, while the location of the guide elements is controlled by features formed in a base portion of the switch body. Having elements that need to work together precisely being dimensionally controlled from separate components of the switch decreases accuracy and is likely to result in uneven wear during use. Accurate assembly is thus made more difficult and time-consuming as well. Additionally, even if perfect alignment is achieved this configuration still generates wear debris that will limit the working life of the switch. Another limit on switch cycle life is a buildup of oxides and other contaminants on switch contact surfaces, preventing reliable conduction. There is a continuing need for an RF switch that combines a high lifetime and high reliability with precision movement and ease of assembly in order to overcome the deficiencies of the prior art.